Nanostructures, such as nanotubes and nanowires, exhibit technologically important electronic properties and have shown promising applications, including nanoscale electronic and optical devices, high strength materials, electron field emission devices, tips for scanning probe microscopy, and chemical sensors. Boron nanostructures have recently attracted much attention because they are predicted to possess special properties superior to those of other one-dimensional nano-materials. For example, boron nanotubes appear to be stable and, independent of structural helicity, have metallic conductivities exceeding those of carbon nanotubes. Metallic nanotubes can carry large current densities and, by themselves, may be useful for providing electrical interconnects and switches.
Boron compounds have also received renewed interest as a result of the discovery of superconductivity in MgB2. Measurements of the upper critical field, Hc2(T), the thermodynamic critical field, Hc(T), and the critical current, Jc, indicate that MgB2 is a type-II superconductor with a superconducting transition temperature of Tc≅40 K and properties that are consistent with an intermetallic superconductor. Measurements of the boron isotope effect in this compound are consistent with the superconductivity being mediated via electron-phonon coupling.
Recent band structure calculations point to the importance of two-phonon pairing for resonant exchange between Cooper pairs in boron compounds such as MgB2. The band structure is also known to depend on the dimensionality of the electron and phonon system. For example, the electron pairing potential can be enhanced in MgB2-nanotubes by several gaps in the phonon density of states, thereby synergetically enhancing both Tc and Jc. Such high-temperature superconductors are expected to be important, for example, for efficient lossless transmission of electric power.
It would therefore be desirable to provide a process for the growth of boron-based one-dimensional and two-dimensional nanostructures, such as nanowires and nanotubes, in particular singe-wall nanotubes, with controlled chemical and physical properties and dimensionality in or on a suitable framework material, as well as devices using such nanowires and nanotubes with properties that are superior to those found in three-dimensional structures made from the same or a similar material.